This study is designed to test the hypothesis that colonial bats are an overwintering reservoir host of eastern equine encephalomyelitis virus in New England. The proposal includes: 1) Virologic and serologic surveillance for evidence of natural infections in colonial bats. 2) Longitudinal viremia studies to determine the levels and duration of virus in the blood and other tissues of active and hibernating bats. 3) Longitudinal antibody studies to determine the levels and duration of complement-fixing, hemagglutination-inhibiting, and neutralizing antibody before, during, and after simulated hibernation. 4) Studies to determine the possible role of interscapular adipose tissue (brown fat) in persistent infections of EEE virus in hibernating bats. 5) Studies to detect possible non-arthropod mechanisms of virus transmission among hibernating bats. 6) Host preference studies to determine the willingness of Culiseta melanura and other potential vector species to engorge on non-hibernating bats under laboratory conditions and to compare the attractiveness of the bat with other vertebrates under field and laboratory conditions. 7) Transmission studies to demonstrate bird-mosquito-bat and bat-mosquito-bird cycles at appropriate seasons of the year.